The present invention relates to a particulate filter for scavenging particulate matters (which will hereinafter be abbreviated to PMs if not especially specified) typified by soot defined as suspended particulate matters contained in an exhaust gas of, e.g., a diesel engine.
The diesel engine has a high economical merit and is, while on the other hand, highly required to purge the exhaust gas of the PMs. What is known for attaining this is a technology of providing a particulate filter for scavenging the PMs in an exhaust system of the diesel engine so that the PMs are not discharged into the atmospheric air (see Japanese Patent Application Laying-Open Publication No.9-262414).
The particulate filter basically includes N-sheets of (N is an even-number of 2 or larger) composed of heat resisting metal fibers and having a filter function, and the same number of heat resisting metal plates as that of the non-woven fabrics, each having a widthwise dimension somewhat smaller than the non-woven fabric, taking a corrugated shape in vertical section and therefore generally called a corrugated sheet.
The following is an outline of the method of forming the particulate filter.
An elongate rectangular multi-layer member is formed by piling up alternately the corrugated sheets and the non-woven fabrics in same direction, and is thereafter wound in roll as to be a cylindrical shape (what the elongate rectangular multi-layer member is formed in the cylindrical shape will hereinafter be called a [cylindrical multi-layer body]).
Note that a configuration of the cylindrical multi-layer body is kept in the cylindrical shape owing to a rigidity of the corrugated sheet. Namely, the corrugated sheet functions as a bone member of the cylindrical multi-layer body.
Then, the cylindrical multi-layer body has a sealing portion that seals by welding the leading edges of the non-woven fabrics adjacent to each other in the radial direction, and a non-sealing portion that keeps open the leading edges of the non-woven fabrics similarly adjacent to each other, these sealing and non-sealing portions being formed alternately.
To describe it in depth, the cylindrical multi-layer body is formed alternately with the sealing portion at which the corrugated sheet positioned between the non-woven fabrics is closed and invisible when viewed from is one side end thereof, and with the non-sealing portion at which the corrugated sheet is visible because of its being opened. Then, the sealing portion and the non-sealing portion are also formed alternately at the other side end thereof. The positions of forming the sealing and non-sealing portions are, however, different at one side end and at the other side end.
Namely, with respect to a couple of adjacent non-woven fabrics with the sealing portions at one side end of the cylindrical multi-layer body, the other side end is provided with no sealing portion. With respect to another couple of adjacent non-woven fabrics with no sealing portion formed at one side end, the other side end is provided with the sealing portion.
As a result, portions with the corrugated sheets inserted into spaces, of which one side end closed and the other side end opened, surrounded by the non-woven fabrics, (hereinafter be called a [layer portion]), are formed spirally in multi-layers in the cylindrical multi-layer body. Then, the thus configured cylindrical multi-layer body is inserted into the heat resisting metal container having substantially the same diameter as an inside diameter of the exhaust pipe and opened at both of side ends thereof. The inner surface of the heat resisting metal container and the outer peripheral surface of the cylindrical multi-layer body, are welded at proper portions, thereby fixing the cylindrical multi-layer body to the heat resisting metal container. The particulate filter is thus formed. Note that the particulate filter is formed so that no gap is formed to the greatest possible degree between the cylindrical multi-layer body and the heat resisting metal container in order to ensure the durability against vibrations.
The particulate filter is attached to the exhaust pipe by fitting the filter into a joint portion between the exhaust pipes.
Further, the heat resisting metal container is charged with the cylindrical multi-layer body so as to not form any gap within the heat resisting metal container, and the exhaust gas flows through the cylindrical multi-layer body without any leakage. It can be therefore said that the outside diameter of the cylindrical multi-layer body has, though slightly smaller, substantially the same dimension as the inside diameter of the heat-resistant metal container.
The thus configured particulate filter attached to the exhaust pipe is coaxial with the exhaust pipe.
Then, in a state where the particulate filter is attached to the exhaust pipe, the exhaust gas flowing through the exhaust pipe towards the particulate filter enters the layer portion from the non-sealing portion provided upstream of the exhaust gas in the non-woven fabric, and thereafter flows downstream of the exhaust pipe. The downstream side within this layer portion is sealed by welding, and extremely minute gaps formed between the fibers of the non-woven fabric are closed at this portion. Accordingly, the exhaust gas flowing nowhere flows from the layer portion sealed downstream towards other layer portion adjacent to the former layer portion and having the non-sealing portion on the downstream side. At this time, the PMs are scavenged in between the minute gaps of the non-woven fabric, thereby purging the exhaust gas of the PMs.
The exhaust gas with the PMs removed flows into the other layer portion and is thereafter, because of the other layer portion with the non-sealing portion provided downstream and opened, discharged into the atmospheric air.
On the other hand, when a quantity of the PMs scavenged by the particulate filter becomes large enough to cause clogging in the metal fiber non-woven fabric, an exhaust resistance rises with the result that the flow of the exhaust gas becomes unsmoothed Besides, no further scavenging of the PMs can be attained.
Such being the case, the scavenged PMs are removed by periodically burning PMs with the heat of the exhaust gas or the heat of an electric heater, etc., thereby preventing the clogging. This serves to eliminate an obstacle against scavenging the PMs by the particulate filter. This is called a recycling of the particulate filter.
By the way, according to the prior art disclosed in Japanese Patent Application Laying-Open Publication No.9-262414, the elongate rectangular multi-layer member composed of the non-woven fabric and the corrugated sheet is wound in roll, and needed to slightly bend a start-of-winding portion of the elongate rectangular multi-layer member because of such a configuration. Therefore, an excessive stress occurs on the bent portion as the start-of-winding portion of the elongate rectangular multi-layer member, and as a result cracks and creases are, though minute, easy to form in that portion.
Further, when forming the cylindrical multi-layer body, though feasible to obtain a strength in the radial direction with the corrugated plate, the non-woven fabric and the corrugated plate are held in the axial direction only by a frictional resistance due to a contact therebetween with only an arrangement that the elongate rectangular multi-layer member is wound in roll by simply piling up the non-woven fabric and the corrugated sheet. Hence, if a pressure of the exhaust gas that acts in the axial direction abruptly changes, a deviation between the non-woven fabric and the corrugated plate might occur. If the deviation therebetween occurs, the rigidity of the cylindrical multi-layer body that is kept by the corrugated plates decreases, and it is considered that the cracks and the damages are caused in the cylindrical multi-layer body.
Next, the particulate filter is, as described above, coaxial with the exhaust pipe, and the outer peripheral portion of the cylindrical multi-layer body is welded to the heat resisting metal container.
On the other hand, the portion exhibiting the highest velocity (i.e., the highest pressure) of the flow of the exhaust gas within the exhaust pipe, is the axial core of the exhaust pipe, and this axial core is the easiest to receive an influence of exhaust pulses defined as pressure wave movements occurred within the exhaust pipe.
Hence, while the particulate filter is used for a long period, the central portion of the cylindrical multi-layer body is thrust downstream due to the influence of the pressure and then protruded, and gets deformed as if a tapered helical spring. Then, if the thrust force acts more than the rigidity of the cylindrical multi-layer body, the particulate filter comes into a fracture.
Further, if the particulate plate is used over a long period of time, it is considered that the welding of the sealing portion provided on the downstream side of the cylindrical multi-layer body, might be taken off due to fluctuations in pressure that are caused by the exhaust heat and the exhaust pulses. As a result, the sealing portion gets open, and this does not make much difference from the exhaust gas just flowing through the particulate filter with nothing obstructing. Then, a rate of scavenging the PMs with the non-woven fabric extremely decrease, and the filter function of the particulate filter might decline.
In addition, the exhaust gas contains a so-called ash having an influence as little as harmless on a human body, which contains, as a main component, calcium sulfur trioxide (lime) defined as a combustible component of the engine oil. The ash is also a substance adhered to the particulate filter. Therefore, if the ash is adhered to the particulate filter, a further increase in the exhaust resistance is brought about. Hence, the ash, if adhered to the particulate filter, is required to be removed.
What can be considered as a removing method thereof is burning that utilizes the heat of the exhaust gas and so on. In the case of the soot as a typical example of the PM, the soot can be burnt with the heat on the order of 600xc2x0 C. However, the ash cannot be burnt if not over 1000xc2x0 C. Besides, if the heat as high as 1000xc2x0 C. is brought into the exhaust system, though the ash can be burnt, thermal damages are exerted on and exhaust system structures such as the particulate filter itself, a catalyst converter, etc.
It is therefore an important subject how the ash is removed from the particulate filter.
The present inventors of this application discovered as a result of having performed repeatedly tests and studies about the particulate filter that a rate of the ashes adhered to the surface of the non-woven fabric differs depending on a difference between metal fibers constituting the non-woven fabric.
Further, the present inventors discovered a specific non-woven fabric capable of remarkably reducing a quantity of deposition of the ash even if less than 1000xc2x0 C. defined as an ash combustible temperature, for example, even at approximately 600xc2x0 C. defined as a soot combustible temperature.
In addition, the present inventors pursued a cause that the ash is not deposited on this specific non-woven fabric, and discovered that the PM typified by the soot and the ash permeate into the fibers of the non-woven fabric.
Moreover, it proved that a void ratio (a ratio of volume of voids contained in the non-woven fabric to unit capacity of the non-woven fabric with respect), and a line diameter and a thickness of the metal fiber of the specific non-woven fabric fall within specified ranges.
Further, the present inventors elucidated the reason why the ash is hard to deposit on the non-woven fabric if at least the void ratio, and the line diameter among the void ratio, the line diameter and the thickness fall within the specified ranges described above.
Still further, since the operation of welding the non-woven fabric for sealing is done at a very minute portion, the operation being simplified as much as possible is also desired.
In addition, generally the exhaust pipe of the internal combustion engine accommodates the heat resisting container, and therefore the container takes a cylindrical shape as its outer configuration. When the cylindrical multi-layer body assuming the similar shape to the cylindrical heat resisting container is inserted into this container, if a dimension of the inside diameter of the heat resisting container is in close proximity to a dimension of the outside diameter of the cylindrical multi-layer body, there arises a problem that these two members are fitted to each other with a difficulty.
Further, it is desirable to provide a technology capable of reducing the number of the recycling processes of the particulate filter.
Moreover, it is considered that a durability of the particulate filter might decline due to an occurrence of the thermal stress caused by a difference in thermal expansion between the exhaust pipe where the particulate filter is disposed and the constructive members of the particulate filter.
It is an object of the present invention, which was devised under such circumstances, to provide a technology capable of, for instance, preventing damages to the particulate filter, removing the ash from the particulate filter without by burning, simplifying the operation of welding the non-woven fabric for sealing, improving an operability by facilitating an insertion of the multi-layer body into the heat resisting container, reducing the number of the recycling processes executed when the particulate matters such as the soot are accumulated on the particulate filter, and enhancing a durability of the particulate filter.
To accomplish the above object, a particulate filter of the present invention adopts the following means.
(1) A particulate filter according to the present invention comprises an axial core composed of a heat resisting metal, a multi-layer body formed by winding the axial core with a multi-layer member into which a non-woven fabric and a corrugated sheet each composed of a heat resisting metal are tiered, and a heat resistant container charged with the multi-layer body.
Herein, the [non-woven fabric] is a fabric formed by mechanically, chemically and thermally processing fiber sheets without taking the form of yarns and joining them by adhesives and a fusing force of the fibers themselves.
Further, as the particulate filter is provided in the exhaust system of the internal combustion engine, said [heat resisting container] is resistible against the high heat of the exhaust gas and has an inlet and an outlet through which the exhaust gas can flow inside. Further, it is desirable that a diameter of the heat resisting metal container be substantially the same as an inside diameter of the exhaust pipe of the engine.
According to the present invention, when forming the cylindrical multi-layer body, the multi-layer member is wound on the axial core. Hence, when starting winding a leading edge of the multi-layer member to be wound on the axial core, a bending degree (curvature) needed to wind the leading edge of the multi-layer member can be set larger by a degree of existence of the axial core than when starting winding the leading edge in a state where there is provided no axial core. Therefore, the minute cracks and creases are hard to occur in the start-of-winding portion (that is, the leading edge) of the multi-layer member, in other words, in the portion of the multi-layer member that comes into contact with the periphery of the axial core when forming the cylindrical multi-layer body by winding the axial core with the multi-layer member. Hence, the durability of the central portion of the cylindrical multi-layer body can be improved.
(2) In the case of the item (1) described above, the multi-layer body takes a cylindrical shape, of which two side ends are formed alternately with a sealing portion for sealing leading edges of the non-woven fabrics adjacent to each other and a non-sealing portion opened in the radial direction, and, with the sealing and non-sealing portions ensured, a bag-shaped layer portion with its one side end closed and the other side end opened is formed.
(3) In the case of the item (1) or (2) described above, it is preferable that the particulate filter further comprises axial core movement preventing means for preventing the axial core from moving in the axial direction within the heat resisting container.
In this case, for example, when the particulate filter is installed in the engine exhaust system, even if a peripheral portion (the central portion of the cylindrical multi-layer body) containing the axial core with respect to the cylindrical multi-layer body receives an influence of the pressure caused by exhaust pulses, etc. and is thrust towards the downstream side, the axial core movement preventing means prevents the axial core from moving. Accordingly, the axial core does not protrude from the heat resisting container, so that the cylindrical multi-layer body gets neither deformed nor fractured. Hence, the particulate filter is not damaged.
(4) In the case of the item (3) described above, it is preferable that the axial core movement preventing means is a connection member for fixedly connecting the heat resisting container to the axial core of the cylindrical multi-layer body.
With this contrivance, when the particulate filter is installed in the engine exhaust system, even if the central portion of the cylindrical multi-layer body is thrust downstream by the influence of the pressure caused due to exhaust pulses, etc., the connection member becomes a hindrance to prevent the movement of the axial core. Accordingly, the axial core does not protrude from the heat resistant container, and the cylindrical multi-layer body gets neither deformed nor fractured. Hence, the particulate filter can be prevented from being damaged.
(5) In the case of the item (4), it is preferable that the heat resistant container is a container of which two side ends are opened, and the connection member is fitted to an opening at one side end of the heat resistant container and includes a ring portion facing to an opening edge of one side end of the heat resistant container, a boss portion facing to the axial core of the cylindrical multi-layer body, and arm portions connecting the ring portion to the boss portion and facing to portions excluding the axial core with respect to the cylindrical multi-layer body.
In this case, the connection member is attached to the opening at one side end of the heat resisting container with both side ends opened, charged with the cylindrical multi-layer body. In the connection member, the boss portion faces to the axial core of the cylindrical multi-layer body and is fixed to the ring portion via the arm portions. Therefore, even if the axial core is thrust downstream by the influence of the pressure due to the exhaust pulses, etc., the axial core impinges on the boss portion. The boss portion is fixed to the ring portion via the arm portions, i.e., the axial core is hindered by the component of the connection member and is unable to move, and hence the whole cylindrical multi-layer body including the axial core at its central portion does not protrude from the heat resistant container. Accordingly, the particulate filter is not damaged.
Further, the number of the arm portions of the connection member is not limited if capable of fixing the boss portion to the ring portion. If the number of the arm portions is too many, however, the arm portions hinder the flow of the exhaust gas, with the result that an exhaust resistance increases. According to the tests performed by the present inventors, approximately four pieces of arm portions are considered preferable.
(6) In the case of the item (5), it is preferable that the boss portion includes a joining portion joining the boss portion to the axial core. With this contrivance, the boss portion is hard to come off the axial core, so that the protrusion of the axial core can be surely restrained.
Note that there can be considered some structures of the joining portion for joining the boss portion to the axial core, however, for example, fitting means for fitting the boss portion to the axial core may be exemplified.
(7) In the case of the item (5) or (6), it is preferable that the arm portion takes a rectilinear shape.
Herein, for instance, a shape like a cross centering the boss portion is preferable as the rectilinear shape.
(8) In the case of the item (5) or (6), it is preferable that the arm portion further takes a curvilinear shape.
A shape like an S-shape centering the boss portion is preferable as the curvilinear shape.
Herein, the arm portion taking the rectilinear shape described above is compared with the arm portion taking the curvilinear shape.
A length of the rectilinear arm portion is shorter than that of the curvilinear arm portion, and therefore a rate of the arm portions facing to the cylindrical multi-layer body is smaller. Hence, it can be said that there is less hindrance against the flow of the exhaust gas, resulting in a decrease in the exhaust resistance. Accordingly, the exhaust gas gains a smooth flow, however, a force for restraining a protrusion of the cylindrical multi-layer body from the heat resistant container decreases.
In the case of the curvilinear arm portions taking the S-shape, a length of each of the arm portions that connect the ring portion to the boss portion is larger than the rectilinear arm portion. Hence, the rate of the arm portions facing to the cylindrical multi-layer body increases, so that there rises the degree to which the flow of the exhaust gas flowing through cylindrical multi-layer body is restrained by the arm portions. Hence, the exhaust resistance increases corresponding thereto. Therefore, the flow of the exhaust gas gets unsmoothed. There, however, increases the force of restraining the protrusion of the cylindrical multi-layer body from the heat resistant container. Further, the curvilinear arm portions take a larger allowable difference in dimension due to the thermal expansion than the rectilinear arm portions, thereby providing a higher usability.
Thus, the rectilinear and curvilinear arm portions have their advantages and disadvantages. Whatever shape the arm portion may take, the boss portion that restrains the movement of the axial core is fixed by the arm portion, so that the strength of the boss portion rises. Further, the force of restraining the central portion of the cylindrical multi-layer body facing the boss portion from protruding downstream out of the heat resistant container rises.
(9) In the case of the item (6), the particulate filter is installed in an exhaust system of an internal combustion engine and used as a scavenger for scavenging mainly particulate matters contained in the exhaust gas, the axial core has a hollow of which two side ends are opened, the hollow containing a partition wall for partitioning the hollow into two, when the particulate filter is installed in the engine exhaust system, the partition wall partitions the hollow into an upstream-sided hollow opened upstream of the exhaust system but closed downstream thereof and a downstream-sided hollow opened downstream but closed upstream, the joining portion serves as a fitting shaft fitted into the downstream-sided hollow, and a substantial lengthwise dimension of the fitting shaft is set somewhat larger than a lengthwise dimension of the downstream-sided hollow, the fitting shaft and the axial core are composed of separate members each having a different elasticity, and a gap is formed between the heat resistant container and the connection member due to a dimensional difference between the lengthwise dimension of the fitting shaft and the lengthwise dimension of the downstream-sided hollow when the fitting shaft is fitted into the down-stream-sided hollow.
Herein, the [substantial lengthwise dimension of the fitting shaft] is a lengthwise dimension of the fitting shaft protruding towards the upstream side of the axial core from the boss portion of the connection member.
According to the present invention, the lengthwise dimension of the fitting shaft is set somewhat larger than the lengthwise dimension of the downstream-sided hollow, and the fitting shaft and the axial core are composed of the separate members each having a different elasticity. When the fitting shaft is fitted into the downstream-sided hollow, the gap is formed between the heat resistant container and the connection member due to the dimensional difference between the lengthwise dimension of the fitting shaft and the lengthwise dimension of the downstream-sided hollow. Therefore, if, for instance, the periodic vibrations caused by the external force, i.e., the vibrations due to the fluctuations in pressure caused by, e.g., the exhaust pulses are transferred to the particulate filter, the axial core easy to largely receive the influence thereof and the fitting shaft fitted into the downstream-sided hollow, oscillate within the gap due to the difference in elasticity therebetween.
Then, the cylindrical multi-layer body including the axial core also oscillates, and hence, if the ash is adhered to the cylindrical multi-layer body at that time, the ash is shaken off, thereby obviating the clogging in the non-woven fabric. Accordingly, the ash can be removed from the particulate filter without by burning.
(10) In the case of the item (9) described above, it is preferable that a plate-like elastic member is interposed in the gap.
Herein, the [elastic member] can be exemplified such as a gasket composed of, e.g., a ceramic fiber. Further, the preferable elastic member has its shape coincident with the connection member.
Then, with this kind of gasket interposed in the gap, it is possible to relax an impact sound emitted when the connection member impinges upon the heat resistant container due to the vibrations. Further, the impact sound is further relieved by properly selecting the material that forms the gasket without being limited to the ceramic fiber, and the clogging can be further prevented.
(11) In the case of the item (3), it is preferable that when installed in the exhaust system of the internal combustion engine, the axial core is formed with a hollow opened upstream thereof and extending downstream in the axial direction, and a through-hole formed through a peripheral wall of the axial core and communicating with the hollow and the multi-layer member along the axial core, and the axial core is thereby provided with the axial core movement preventing means.
In this case, the exhaust gas flows into the hollow within the axial core from the open side end provided by making open the upstream-side end of the axial core, and flows out to the multi-layer member along the axial core via the through-hole. The exhaust gas flowing out to the multi-layer member is discharged into the atmospheric air from the adjacent bag-shaped layer portion surrounded by the non-woven fabric and formed with the non-sealing portion provided downstream.
Therefore, the exhaust gas flows out to the multi-layer member along the axial core, i.e., to the bag-shaped layer portion adjacent most to the axial core via the through-hole of the axial core. With this exhaust gas, the axial core is correspondingly hard to receive the external force such as the pressure of its being thrust downstream of the exhaust gas. Accordingly, the axial core can be prevented from protruding out of the heat resistant container. Hence, there does not occur the damages to the particulate filter due to the deformation and the fracture of the cylindrical multi-layer body.
(12) In the case of the item (11), it is preferable that the through-hole is an oblique hole formed obliquely in the axial core in a way that extends from the upstream side of the engine exhaust system toward the downstream side thereof, and an upstream-sided opening thereof is disposed on the side of the hollow, and a downstream-sided opening thereof is disposed on the side of the multi-layer member wound on the axial core.
With this arrangement, the exhaust gas flowing to the axial core from upstream of the engine exhaust system more smoothly flows through the through-hole than in the case of the through-hole holed at the right angle to the central axis of the axial core.
Namely, the exhaust gas becomes much easier to flow out to the multi-layer member along the axial core, i.e., to the bag-shaped layer portion adjacent most to the axial core via the through-hole of the axial core. With the exhaust gas, it is therefore possible to correspondingly reduce the external force such as the pressure of thrusting the axial core towards the downstream side of the exhaust gas. Hence, the stress occurred on the axial core can be correspondingly decreased. Therefore, it is feasible to decrease the pressure of thrusting downstream the central portion of the cylindrical multi-layer body including the axial core, so that the damage to the particulate filter can be further prevented.
(13) A particulate filter according to the present invention comprises an axial core composed of a heat resisting metal, a multi-layer body formed in a cylindrical shape by winding the axial core with a multi-layer member into which a non-woven fabric and a corrugated sheet each composed of a heat resistant metal are layered, and a heat resisting container charged with the cylindrical multi-layer body, wherein when installed in an exhaust system of an internal combustion engine, the axial core is formed with a hollow opened downstream thereof and extending upstream in the axial direction, and a through-hole formed through a peripheral wall of the axial core and communicating with the hollow and the multi-layer member along the axial core.
In this case, the peripheral wall of the axial core has the through-hole communicating with the hollow and the multi-layer member along the axial core, so that the exhaust gas flowing into the cylindrical multi-layer body contains the exhaust gas flowing into the hollow from outside of the axial core via the through-hole. Therefore, a quantity of the exhaust gas flowing into the cylindrical multi-layer body decreases by a quantity of the exhaust gas flowing into the hollow, and the exhaust gas pressure at the portion formed with the cylindrical multi-layer body using the multi-layer member decreases correspondingly.
Hence, the pressure on the non-woven fabric of the cylindrical multi-layer body is reduced, and hence the welding of the sealing portion secured even by this welding is not taken off. Accordingly, this is effective in preventing the damage to the particulate filter.
Note that there arises such skepticism that the exhaust gas flowing into the hollow of the axial core via the through-hole might be discharged into the atmospheric air in a state where the no-woven fabric does not sufficiently scavenge the PMs. The multi-layer member wound on the axial core, however, covers also the through-hole. Hence, the exhaust gas, after flowing through the through-hole, flows through the non-woven fabric defined as the constructive member of the multi-layer member. Consequently, there is no necessity of having such a concern that the PMs contained in the exhaust gas discharged into the atmospheric air via the hollow of the core through the through-hole, might not be scavenged.
(14) In the case of the item (13), it is preferable that the through-hole is an oblique hole formed obliquely in the axial core in a way that extends from the upstream side of the engine exhaust system toward the downstream side thereof, and an upstream-sided opening thereof is disposed on the side of the multi-layer member wound on the axial core and a downstream-sided opening thereof is disposed on the side of the hollow.
In this case, the exhaust gas flowing towards the axial core from the multi-layer member flows through the through-hole more smoothly than in the case of the through-hole being holed at the right angle to the central axis of the axial core, and enters the hollow. Namely, the exhaust gas pressure at the portion formed with the cylindrical multi-layer body using the multi-layer member is further reduced. As a result, correspondingly a larger amount of exhaust gas can be discharged into the atmospheric air via the through-hole, so that a load upon the sealing portion can be further reduced. This is therefore further effective in preventing the damage to the particulate filter.
(15) In the case of the items (11) through (14), it is preferable that a rate at which a diameter of the axial core occupies a diameter of the cylindrical multi-layer body is within a range of 15 to 27%.
If the diameter of the axial core falls within this range, in the case of the items (11) and (12) described above, it proved from the tests performed by the present inventors that the force of thrusting the axial core is effectively reduced.
Further, if the diameter of the axial core falls within this range, in the case of the items (13) and (14) described above, it proved from the tests performed by the present inventors that the pressure applied on the non-woven fabric is decreased.
(16) A particulate filter according to the present invention comprises an axial core composed of a heat resisting metal, a multi-layer body formed by winding the axial core with a multi-layer member into which a non-woven fabric and a corrugated sheet each composed of a heat resisting metal are tiered, and a heat resisting container charged with the multi-layer body, wherein the multi-layer member has the corrugated sheets disposed on one surface of the non-woven fabric folded double in a widthwise direction so as to take a folded shape and at a portion between the folded surfaces.
The particulate filter according to the present invention is configured such that the multi-layer member wound on the heat resisting metal axial core to form the cylindrical multi-layer body, has the corrugated sheets disposed respectively on one surface of the non-woven fabric folded double in the widthwise direction in a folded shape and at a portion between the folded surfaces thereof. Then, the multi-layer member simply wound in roll has its one side end that is all in a non-sealing state at this stage. At the other side end thereof, however, the portion including the creases of the non-woven fabric, in other words, the portion corresponding to a boundary line between the two surfaces facing to each other in the folded non-woven fabric, is already substantially in the sealing state. Therefore, the necessity for the welding operation for forming the sealing portion can be eliminated correspondingly. Note that the folded non-woven fabric is wound in roll, so that the portion between substantially the sealing portions is the non-sealing portion.
Hence, the welding operation for forming the sealing portion may be done for only one side end of the multi-layer member wound in roll, so that the operation efficiency is highly improved. Note that the [crease] is not limited to a distinctive crease formed when folding the non-woven fabric, and a side portion formed with some width when folding back the non-woven fabric without the distinctive crease may come under the category of the [crease].
(17) In the case of the item (16) described above, it is preferable that the particulate filter is installed in an exhaust system of an internal combustion engine and used as a scavenger for scavenging mainly particulate matters contained in the exhaust gas, and is also installed in the engine exhaust system in a state where the creases of the folded non-woven fabric are directed downstream of the engine exhaust system.
In this case, the creased portion does not require the welding for sealing as explained above. Hence, the creased portion is not formed by making integral the originally separate non-woven fabrics adjacent to each other by welding as in the case of the conventional non-woven fabrics. Therefore, even if the fluctuations in pressure due to the exhaust heat and the exhaust pulses act on the creased portion, this creased portion does not open. Hence, it is feasible to prevent the PM scavenging rate from extremely decreasing.
(18) In the case of the item (17), a bag-shaped layer portion with its one side end closed and the other side end opened is formed by alternately forming a sealing portion for sealing leading edges of the non-woven fabrics adjacent to each other in the radial direction on one side end side of the multi-layer member and a non-sealing portion opened.
(19) In any one case of any one the items (1) through (18), it is preferable that the particulate filter is installed in an exhaust system of an internal combustion engine and used as a scavenger for scavenging mainly particulate matters contained in the exhaust gas, and, in this case, a flow-past hole that lets the exhaust gas through is formed at a downstream-sided end of a narrower passageway than other passageways among the passageway within the particulate filter through which the exhaust gas flows.
Herein, the [passageway within the particulate filter through which the exhaust gas flows] includes not only the air space surrounded by the non-woven fabrics contained in the cylindrical multi-layer body, i.e., the bag-shaped layer portion with one side end closed and the other side end opened, but also the air space formed outermost between the cylindrical multi-layer body and the heat resistant container. The air space disposed outermost is generally narrower than the air space surrounded by the non-woven fabrics contained in the cylindrical multi-layer body. This is because if the air space formed between the inner surface of the cylindrical multi-layer body and the outer surface of the heat resistant container is large, the cylindrical multi-layer body is easy to impinge on the heat resistant container due to the vibrations, and the above contrivance intends to prevent this impingement. Further, with this structure taken, the capacity of the cylindrical multi-layer body can be made as larger as possible, a PM scavenging area widens, with the result that the exhaust resistance when scavenging the PMs can be decreased.
A fluid flows first to a wide area and to a narrow area afterward. Namely, to describe it in the case of the exhaust gas flowing through the particulate filter, the exhaust gas does not flow through the narrow passageway until it comes to a state the ashes and PMs form the clogging at first in the wide passageway and the exhaust gas can not flow through this wide passageway anymore. Hence, if there is provided the flow-past hole through which the exhaust gas can flow straight to the downstream side of the narrow passageway through which to flow the exhaust gas, even if the clogging is caused, the exhaust gas flows straight through this flow-past hole, so that any damage to the particulate filter is not brought about.
However, there is a problem that is caused by only passing the exhaust gas through the narrow passage because the passage is narrow, even if a quantity of the exhaust gas flowing therethrough is small. Accordingly, it is of importance that a recycling of the particulate filter is performed before the exhaust gas flows through the flow-past hole.
(20) In the case of the item (19), it is preferable that the narrow passageway is filled with a porous substance having the maximum void ratio at which the particulate matters can be scavenged.
With this contrivance, the exhaust gas is made to simply pass through the narrow passageway, and besides it is possible to scavenge at least the PMs.
(21) A particulate filter according to the present invention comprises an axial core composed of a heat resisting metal, a multi-layer body formed in a truncated cone shape by winding the axial core with a multi-layer member into which a non-woven fabric and a corrugated sheet each composed of a heat resisting metal are tiered, and a heat resistant container charged with the multi-layer body taking the truncated cone shape.
The heat resisting container is generally accommodated in the exhaust pipe of the internal combustion engine and therefore takes the cylindrical shape in its outer configuration. Because of this configuration, the cylindrical multi-layer body is inserted into the cylindrical heat resisting container with a difficulty. The multi-layer member of the particulate filter according to the present invention, however, takes the truncated cone shape, and therefore the leading edge of the multi-layer body is hard to come into contact with the heat resistant container. Hence, the advantage is that the multi-layer body is easily inserted into the heat resistant container.
(22) In the case of the item (21), the truncated cone-shaped multi-layer body has its two side ends formed alternately with a sealing portion for sealing leading edges of the non-woven fabrics adjacent to each other and a non-sealing portion opened in the radial direction. With the sealing and non-sealing portions ensured, a bag-shaped layer portion with its one side end closed and the other side end opened, having a inclined surface taking a fan shape from the closed side towards the opened side, and the corrugated plate is disposed in a fan-shape corresponding to the fan-shaped inclined surface within the layer portion.
On the other hand, in the case where the particulate filter scavenges the PMs, if the multi-layer body takes the cylindrical shape, the PMs tend to concentrate comparatively on the downstream side in the flowing direction of the exhaust gas in the bag-shaped layer portion, so that the clogging of the non-woven fabric is easy to occur at this portion. Hence, if there excessively increases the stress at the portion, where the clogging easily occurs, in the bag-shaped layer portion, the stress greater than the rigidity us generated at the tail edge of the bag-shaped layer portion, resulting in a damage such as a fracture to this tail edge.
In the particulate filter of the present invention, however, the tail edge of the bag-shaped layer portion is larger (wider) than the leading edge and therefore has a higher rigidity. Hence, the bag-shaped layer portion has an increased rigidity on its downstream side. For this reason, even if the pressure on the downstream side of the bag-shaped layer portion rises when scavenging the PMs on the downstream side, there is no possibility in which the crack and damage occurs in the high-pressure portion because of this portion securing the high rigidity.
Further, the bag-shaped layer portion includes the fan-shaped inclined surface, so that a flowing force of the exhaust gas impinging obliquely upon the inclined surface is decomposed into a component force (vertical component force) vertical to a thicknesswise direction of the bag-shaped layer portion, and a component force (parallel component force) parallel to the surface of the bag-shaped layer portion.
On the other hand, when the multi-layer body takes the cylindrical shape as described above, the exhaust gas entering in the longitudinal direction of the bag-shaped layer portion impinges on the tail edge of the bag-shaped layer portion, and the PMs are gradually scavenged by the non-woven fabric. Especially the leading edge (downstream side) of the non-woven fabric forming the bag-shaped layer portion, however, the PMs are hardly scavenged.
By contrast, according to the particulate filter of the present invention, as described above, the bag-shaped layer portion has the fan-shaped inclined surface, so that the flowing force F of the exhaust gas impinging upon the leading edge of the non-woven fabric is decomposed into the vertical component force and the parallel component force. With the action of the vertical component force, the exhaust gas flows to respective areas within the non-woven fabric. Hence, it is possible to scavenge the PMs substantially uniformly over the whole non-woven fabric. It is therefore feasible to highly effectively restrain the occurrence of the clogging in concentration on the tail edge side of the bag-shaped layer portion.
If the clogging is caused in concentration at one portion of the bag-shaped layer portion as at the tail edge of the bag-shaped layer portion, the recycling process of the particulate filter must be executed each time. The particulate filter of the present invention is, however, capable of scavenging the PMs substantially uniformly over the whole non-woven fabric, and hence there may be correspondingly a less frequency of executing the recycling process of the particulate filter.
The recycling process is, as already described, the process for eliminating a trouble in the PM-scavenging of the particulate filter by periodically burning and thus removing the scavenged PMs in a way that makes the use of the heat of the exhaust gas and of the electric heater, etc. and thereby preventing the clogging. Therefore, it can be understood that a decreased frequency of executing this recycling process leads to an improved fuel consumption, and works highly effectively on reducing a quantity of the power consumption.
Based on such a point of view, the particulate filter is installed in the exhaust system. In this case, the following structure may be taken.
(23) In the case of the item (22), the particulate filter is attached to the exhaust system in a state where a large-diameter portion of the truncated cone-shaped multi-layer body is positioned downstream of the exhaust system. With this structure taken, the stress applied on the non-woven fabric disposed outermost of the multi-layer body becomes a compression stress due to the pressure of the exhaust gas. Reversely when attached on the upstream side, the stress on the non-woven fabric becomes a tensile stress. It is known from the tests performed by the present inventors that the non-woven fabric has a greater compression intensity than a tensile intensity, and the former structure described above improves the durability against the pressure of the exhaust gas.
(24) In the case of any one of the items (2) to (12), (19), (20) and (23), it is preferable that plural sheets of non-woven fabrics each having a different void ratio are layered integrally into one sheet of non-woven fabric taking a multi-layered structure, the multi-layer body is composed of the non-woven fabric and the corrugated plate, and the non-woven fabric taking the multi-layered structure with respect to the bag-shaped layer portion defined as a constructive member of the multi-layer body is formed so that an void ratio of the single non-woven fabric decreases stepwise from the single non-woven fabric disposed on an inlet side of the exhaust gas towards the single non-woven fabric disposed on an outlet side of the exhaust gas.
In the particulate filter of the present invention, the void ratio is not uniform but gradually decreases from the exhaust gas inlet side of the non-woven fabric towards the exhaust gas outlet side thereof. The PM having a comparatively large particle size is scavenged by the non-woven fabric having the large void ratio, and the PM having a small particle size is scavenged by the non-woven fabric having the small void ratio. The PM having an intermediate particle size is scavenged by the non-woven fabric the intermediate void ratio. Therefore, the PMs are scavenged uniformly over the whole non-woven fabric without concentrating on one portion of the non-woven fabric.
(25) In the case of any one of the items (1) through (24), it is preferable that the non-woven fabric is formed so that a line diameter of the metal fiber constituting the non-woven fabric is set within a range of 10 to 50 xcexcm, and the void ratio defined as a capacity ratio of the gaps contained therein to a unit volume of the non-woven fabric is set to any one of the void ratios within a range of 50 to 85%.
It is understood from the tests carried out by the present inventors that when the line diameter and the void ratio fall within these ranges, the ashes are deposited with the difficulty, and that the ashes produced permeate into the metal fibers. If the void ratio is changed stepwise, it is desirable that the void ratio be set within the following range.
(26) In the case of the item (24), the stepwise change in the void ratio is set within a range of 80 to 60%.
(27) In the case of the items (25) and (26), it is preferable that a thicknesswise dimension of the non-woven fabric is within a range of 0.2 to 1.0 mm.
In this case, the thickness of the non-woven fabric applied to the multi-layer member may fall within the dimension range described above irrespective of whether the non-woven fabric takes the multi-layered structure or the mono-layered structure.
(28) In the case of any one of items (2) through (12), (18) through (21), and (25), it is preferable that two sheets of non-woven fabrics each having a different void ratio are layered integrally into one sheet of non-woven fabric taking a two-layered structure, the multi-layer body is composed of the non-woven fabric and the corrugated sheet, and the non-woven fabric taking the two-layered structure with respect to the bag-shaped layer portion defined as a constructive member of the multi-layer body is formed so that an void ratio of the non-woven fabric disposed on the inlet side of the exhaust gas than that of the non-woven fabric disposed on the outlet side of the exhaust gas.
In this case also, the approach is the same as that shown in the item (24), wherein the PMs can be scavenged uniformly over the whole non-woven fabric without concentration on one portion of the non-woven fabric.
(29) In the case of the item (28), it is desirable that the void ratios of the non-woven fabrics disposed on the inlet and outlet sides of the exhaust gas are set to 80% and 60%, respectively. The tests by the present inventors prove that if the void ratio falls within this range, there is shown a high efficiency of scavenging the PMs.
(30) In the case of any one of the items (2) through (12), (18) through (20), and (24), it is preferable that the non-woven fabric takes an integral hierarchical structure of which the void ratio changes stepwise, the multi-layer body is composed of the non-woven fabric and the corrugated sheet, and the non-woven fabric with respect to the bag-shaped layer portion defined as a constructive member of the multi-layer body is formed so that the void ratio gradually decreases from the inlet side of the exhaust gas towards the outlet side of the exhaust gas.
In this case, the arrangement is not that the plurality of non-woven fabrics each having a different void ratio are layered integrally into one sheet of non-woven fabric but that the void ratio is changed within one sheet of non-woven fabric. The effect thereof is not limited to the effect given in the item (24) described above but embraces an effect that the plural sheets of single non-woven fabrics are not required to be combined into one sheet of non-woven fabric, and therefore the operation efficiency can be enhance correspondingly.
(31) In the case of the item (30), it is desirable that the void ratio changes so as to gradually decrease within a range of 80% to 60%. If the void ratio is within this range, the tests by the present inventors proved that there is shown the high efficiency of scavenging the PMs.
(32) In the case of any one the items (1) through (31), it is desirable that an opening edge of one side end of the heat resistant container charged with the multi-layer body is provided with a supporting member for supporting the multi-layer body in the heat resistant container.
Herein, the supporting member is not schemed to make the multi-layer body unmovable by fixing it to the heat resistant container. The supporting member is provided with a scheme of obviating the clogging in the non-woven fabric by shaking off the ashes adhered to the cylindrical multi-layer body in a way that oscillates the multi-layer body with the vibrations such as the pulses. Hence, the supporting member may be exemplifies as follows.
(33) In the case of the item (32) given above, it is desirable that the supporting member includes a holding piece for supporting an outer peripheral edge of the multi-layer body in a state where the outer peripheral edge is sandwiched in between the heat resistant container and the holding piece itself.
(34) In the case of the items (1) through (33), it is desirable that the particulate filter is installed in an exhaust collective pipe.
(35) In the case of the items (1) through (34), the particulate filter is installed in an exhaust pipe, and an adiabatic space is provided between the exhaust pipe and the cylindrical multi-layer body. A size of an adiabatic space formed between the exhaust pipe and the cylindrical multi-layer body is determined a size of an interval between the inside diameter of the exhaust pipe and the outside diameter of the heat resistant container.
In this case, the adiabatic space serves to restrain an occurrence of a thermal stress caused due to a difference in thermal expansion between the cylindrical multi-layer body rising in temperature when burning the PMs and the exhaust pipe exposed to the outside. Further, the periphery of the cylindrical multi-layer body is surrounded with the adiabatic space, thereby enhancing a temperature retaining capacity when burning the PMs so as to burn the PMs at a high efficiency.
(36) In the case of the item (35), the cylindrical multi-layer body is inserted into a cylindrical member composed of a heat resistant metal, and an adiabatic space is provided between the cylindrical member and the heat resistant container. Namely, in this case, the adiabatic spaces are provided between the cylindrical multi-layer body and the heat resistant container, and between the heat resistant container and the exhaust pipe.
A size of the adiabatic space formed between the cylindrical member and the heat resistant container is determined by a difference in dimension between the outside diameter of the cylindrical member and the inside diameter of the heat resistant container. Then, it is preferable that the sealing is provided at the downstream-sided end of the adiabatic space formed between the cylindrical member and the heat resistant container so that the exhaust gas is not discharged directly into the atmospheric air.
Further, it is desirable that the cylindrical member is thick enough to support the cylindrical multi-layer body, and that a heat capacity thereof is as small as possible. The tests performed by the present inventors proved that the thicknesswise dimension thereof is, it is preferable, 0.2 to 2 mm.
(37) In the case of the item (36) given above, it is more effective that a reinforced member is inserted into the adiabatic space. The reinforced member is inserted into the adiabatic space, thereby enhancing a stability of the cylindrical multi-layer body because of being capable of supporting the cylindrical multi-layer body in the axial direction, and enhancing also the durability against the vibrations.
Moreover, it is preferable that the reinforced member is composed of a tree-dimensional metal porous member, wire-netting, a metal non-woven fabric, a corrugated sheet, a metal sheet taking an elongate rectangular shape and a punching metal each having a material filling rate of 30% or less in order not to deteriorate the adiabatic property of the adiabatic space.
Further, the generation of the thermal stress is restrained and the enhancement of the durability can be further expected by equalizing the thermal capacities per volume with respect to the reinforced material, the cylindrical member and the cylindrical multi-layer body.
(38) In the case of the items (1) through (37) described above, it is preferable that the multi-layer body is formed by joining the non-woven fabric and the corrugated sheet each defined as the constructive member thereof. That is, it is preferable that the elongate rectangular multi-layer member composed of the corrugated sheet and the non-woven fabric is wound in roll on the axial core, and thereafter the multi-layer member is formed by joining the contact portion between the corrugated sheet and the non-woven fabric.
A deviation in the axial direction can be prevented by joining the contact portion. Further, the deviation is hard to occur, and it is therefore feasible to prevent a decline of rigidity of the cylindrical multi-layer body. Accordingly, neither the cracks nor the damage is caused in the cylindrical multi-layer body.
(39) In the case of the item (38), the non-woven fabric and the corrugated sheet are joined by diffusion joining.
Herein, the [diffusion joining] is that two sheets of metals to be joined, i.e., the non-woven fabric and the corrugated sheet are layered together, and held by heating at a proper temperature in a pressurized state and thus joined. When joined by this type of diffusion joining, if a raw material of the corrugated sheet and a raw material for the non-woven fabric are substantially the same, the materials are uniformized by a diffusing phenomenon, resulting in a decrease in the stress due to the difference in thermal expansion between the corrugated sheet and the non-woven fabric. The durability can be therefore improved.
(40) In the case of the item (5), it is preferable that the arm portions are formed so that the arm portions face to the portion formed of the multi-layer member of the cylindrical multi-layer body when the connection member is attached to the opening of one side end of the heat resistant container.
When the exhaust gas is discharged, the axial pressure acts not only on the axial core as one of the constructive member of the cylindrical multi-layer body but also on the non-woven fabric and the corrugated sheet of the cylindrical multi-layer body, with the result that the non-woven fabric or the corrugated sheet might protrude from the heat resistant container. The axial deviation of the non-woven fabric and/or the corrugated sheet can be prevented by adopting such a structure that the members as the components of the multi-layer member of the cylindrical multi-layer body, i.e., the non-woven fabric and/or the corrugated sheet face to (supported by) the arm portions.
Normally, the corrugated sheet is shorter in its axial length than the non-woven fabric. Therefore, when the corrugated sheet is supported by the arm portions, the arm portions are required to have a form adapted so that the corrugated sheet are brought into contact with the arm portions. The corrugated sheet does not slide toward the exhaust side by supporting the corrugated sheet on the arm portions. Hence, there is no portion where the non-woven fabric is not supported. It is therefore possible to prevent the decrease in the rigidity of the cylindrical multi-layer body.
Further, there increases the number of the portions where the non-woven and/or the corrugated sheet is supported, so that the stress generated in the axial direction can be dispersed, and the durability of the particulate filter is improved.
(41) In the case of the item (1), it is preferable that a sealing portion for sealing the leading edges of the non-woven fabrics adjacent to each other and a non-sealing portion opened are alternately formed at both side ends of the multi-layer member in the radial direction, and the non-woven fabric and the corrugated sheet are fixed in a state where an axial side end portion of the corrugated sheet is sandwiched in between the non-woven fabrics formed with the sealing portion.
In this case, if the non-woven fabric and the corrugated sheet are fixed by welding and so on in the state where the side end of the corrugated sheet in the axial direction is sandwiched in between the non-woven fabrics forming the sealing portion, the stress in the axial direction of the multi-layer body that occurs on the non-woven fabric can be received by the corrugated sheet. Therefore, the rigidity of the cylindrical multi-layer body is improved, and it is possible to prevent the cylindrical multi-layer body from deviating downstream and protruding by the pressure of the exhaust gas. Moreover, the corrugated sheet receives the stress generated by the pressure of the exhaust gas and applied on the non-woven fabric, and hence the welding of the sealing portion on the downstream side can be prevented from being taken off.
(42) In the case of the items (1) through (41), it is preferable that the axial core has a joining portion partially fixed by welding to the non-woven fabric, and a metal quantity per unit area of the axial core at this joining portion is substantially the same a metal quantity per unit capacity of the non-woven fabric.
With this contrivance, a thermal expansion coefficient of the joining portion of the axial core is equalized to a thermal expansion coefficient of the portion coming into contact with the joining portion of the non-woven fabric. Even if the joining portion of the axial core and the portion of the non-woven fabric that comes into contact with this joining portion receives the heat of the exhaust gas and get deformed, the degrees of these deformations are the same. Therefore, it is feasible to restrain the generation of the thermal stress at the joining portion, and the durability of the joining portion, more essentially, the particulate filter.
For satisfying the requirements described above, if the axial core is large in thickness, the particulate filter is increased in size. Whereas if too thin, the rigidity of the axial core decreases, so that the thickness of the axial core is preferably 0.1 to 0.3 mm.